The invention relates to an apparatus for controlling the electric current through an inductive consumer such as a fuel metering valve for an internal combustion engine.
A series circuit comprising the consumer, current resistor and switch between the supply voltage terminals is known, wherein the consumer and the resistor are bridged by a freerunning circuit. The current-switching device is switched ON and OFF in accordance with the flow of current through the measuring resistor in series with the consumer.
It is disadvantageous in this known circuit lay-out that the potentials at the measuring resistor are raised or lowered each time a switchover takes place by an amount of virtually the entire battery voltage. In order to evaluate these signals, quite expensive circuitry is required.
A current-control apparatus has already been proposed which has one measuring resistor each in the main current circuit and in the freerunning circuit. In this apparatus, the voltage drop over each of the two resistors is detected with a separate threshold switch, and their output signals are utilized for the control of the current-control device. In this proposed apparatus, the two current-measuring resistors may be of different dimensions; thus the resistor in the freerunning circuit can also be of larger dimensions than the resistor in the main current circuit, for the purpose of furnishing a more unequivocal signal in the lower current range.
It is one of the objects of the invention to create an apparatus for controlling the electric current through an inductive consumer in which precisely determinable electrical values appear, which are therefore also capable of being precisely processed, on the one hand, while on the other hand the apparatus is favorable in cost.